1. Field of the Invention
The present invention relates to a printing apparatus and a sheet processing apparatus that have a decurling mechanism.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2009-242008 discloses a decurling device that is employed in a printing apparatus and corrects the curl of a rolled long continuous sheet. This device wraps the sheet around a shaft-like correcting member of a decurling unit at a predetermined wrapping angle, thereby exerting a force that corrects the curl (decurling force) on the sheet.
In a printing apparatus, a rolled sheet is generally cut by a cutter after printing, and the unused region of the sheet is returned and wound. Decurling force also acts on the sheet during this return because a region of the sheet within a predetermined distance from the cut edge passes through the decurling unit. In the case where printing is performed again, the sheet is fed to the printing unit again. Also in this case, decurling force acts on the sheet. If decurling force acts on the same region every time the sheet moves back and forth, excessive decurling may curl the sheet in the opposite direction from the original curl. If the sheet that is significantly curled in the opposite direction is supplied to the printing unit, the leading edge of the sheet may come into contact with the print head. If the sheet comes into contact with the print head, unexpected ink may adhere to the sheet, or the print head and the sheet may be damaged.